1. Field of the Invention
The present invention relates to an apparatus for the contactless measurement of geometrical dimensions.
2. Description of the Prior Art
An apparatus of this type is known from German Offenlegungsschrift No. 28 10 192. In that apparatus, a focused light beam is projected from an emitter initially onto a deflector which rotates about an axis extending perpendicular to the axis of the light beam. The deflector projects the light beam onto an object to be measured in the same plane. The light beam is deflected by this object and is conducted to another rotating deflector from which the light beam is then conducted to a light-sensitive receiver. The deflector assigned to the receiver rotates about an axis which extends parallel to the axis of rotation of the deflector assigned to the emitter, however, the deflector assigned to the receiver rotates at a higher rate of rotation. The light beam is always conducted only in a single plane.
Since the distance between the axes of rotation of the deflectors is known, the angular positions of the deflectors relative to the object to be measured can be used, by an electronic evaluating system forming part of the apparatus, to determine, on the basis of the triangulation method within the given system of coordinates, the position of the point projected by the light beam on the object to be measured.
The known apparatus described above has the disadvantage that the light beam is conducted within a single plane. This means that the light beam emitted by the emitter usually does not meet the axis of rotation of the deflector assigned to the emitter. This is due to unavoidable technical deficiencies, such as, manufacturing tolerances, bearing play or the like. As a result, the direction of the beam deflected by the deflector does not coincide with the ideal direction. The angle error which is caused by this would be negligible if the sector covered by the light beam on the object to be measured were relatively small, i.e., if incoming and outgoing angles are small. However, when these angles increase, the inaccuracy of measurement also increases, particularly in the end locations of the sector covered by the light beam. Thus, in the known apparatus, the measuring accuracy is essentially satisfactory only if it is possible to move an object to be measured into the central range of the light beam sector.
Of course, it is possible to calibrate the known apparatus in order substantially to eliminate errors due to, for example, manufacturing tolerances or bearing play. However, the disadvantage of calibration resides in the fact that it is not only time-consuming and technically cumbersome, but is also relatively easily eliminated by external influences, such as, vibrations, impacts or the like.
It is, therefore, the primary object of the present invention to improve the apparatus of the type described above in such a way that in an apparatus of relatively simple construction a continuous contactless measurement can be ensured even over longer periods of time without calibration or re-calibration.